This invention relates generally to electrical connectors and, more specifically, to an electrical connector of the resilient spring type and particularly adapted for use with conductors formed of a relatively soft, deformable metal such as aluminum.
Numerous electrical connector constructions are known for connecting electrical conductors to one another or to the terminals of electrical devices. In one of the more common constructions, the bared end of an electrical wire is inserted into a connector and a screw, which is threadedly received in the connector, is tightened against the wire so that the wire is held in physical contact with an opposed conductive terminal strap. For years, connectors of this type have been used quite successfully with copper or a copper alloy conductors and connector parts. However, with the introduction of lower cost aluminum conductors and connector parts, attempts to use connectors of the above type have given rise to problems.
Specifically, aluminum, though cheap, is substantially more soft and deformable than copper. Aluminum conductors or connector parts thus have a tendency to deform under the compressive force of the connector screw. This deformation, in time, can cause sufficient loosening of the connection to provide a very high resistance contact. Excess heat is then generated at the connector, which, if unchecked, can destroy the contact completely. If the loosening at the connection is sufficient, electrical arcing can also occur. In either case, not only is the reliability of the connection destroyed, but also a serious fire hazard is presented.
A variety of resilient spring type electrical connectors have previously been proposed for use with aluminum conductors or connector parts. However, none of these connectors have found wide spread commercial acceptance. Several reasons apparently account for this lack of acceptance.
Firstly, many of the proposed connectors are simply not totally effective in solving the deformation problem encountered with aluminum conductors. Connectors are known, for example, which combine a spring metal washer, a resilient pressure pad or a resilient threaded insert with a connector screw which is tightened to clamp a conductor. When the connector screw is initially tightened against the conductor, the washer, pressure pad or insert, as the case may be, is compressed. As the conductor deforms, the washer, pressure pad or insert expands to maintain electrical contact therewith. Problems arise, however, because the washers, pressure pads or inserts typically employed in these connectors have only a limited range of expansion. Thus, while the initial stages of the conductor deformation are accommodated, larger conductor deformations are not. Conductors of this type thus serve only to delay the deformation problems encountered by conventional, rigid connectors.
Other known resilient spring type connectors, while effective in accommodating conductor deformation, have relatively complex constructions. The complexity of construction adds considerably to the cost of manufacturing these connectors. Moreover, it is difficult and impractical in many cases to manufacture these complex connectors in small, compact sizes for use, for example, with small gauge wires or in electrical devices in which the available space is limited.
Finally, many known resilient spring type connectors are not structurally compatible with presently available and installed electrical devices, such as electrical meters, panel boxes and the like. To incorporate the known resilient spring type connectors in these devices would typically require detailed design and manufacturing changes in the devices themselves. These changes would best be made by the manufacturer in new, replacement devices, and even then at considerable cost. To convert already installed devices on a device-by-device basis would be impractical.
It is, therefore, a primary object of this invention to provide an improved electrical connector.
Another object of this invention is to provide an improved resilient spring type electrical connector which is particularly useful with conductors formed from a relatively soft, deformable metal such as aluminum.
Another object of the invention is to provide an electrical connector of the type described which is simple in construction and inexpensive to manufacture.
Another object of the invention is to provide an electrical connector of the type described which, when tightened against a conductor, is capable of expanding over a relatively broad range to accommodate large deformations of conductors with time.
Yet another object of the invention is to provide an electrical connector of the type described which can readily be formed into any of a wide variety of sizes.
Still another object of the invention is to provide an electrical connector of the type described which can be formed by a relatively simple modification of the rigid screw type connectors widely in use in presently installed electrical devices.